1. Field of the Disclosure
The technology of the disclosure relates to dynamic cell bonding (DCB) and, more specifically, to the use of DCB to compensate for the bandwidth limitations of multi-mode optical fiber (MMF).
2. Technical Background
Wireless communication is rapidly growing, with ever-increasing demands for high-speed mobile data communication. As an example, so-called “wireless fidelity” or “WiFi” systems and wireless local area networks (WLANs) are being deployed in many different types of areas (coffee shops, airports, libraries, etc.). Wireless communication systems communicate with wireless devices called “clients,” which must reside within the wireless range or “cell coverage area” in order to communicate with the access point device.
One approach to deploying a wireless communication system involves the use of “picocells.” Picocells are radio frequency (RF) coverage areas having a radius in the range from about a few meters up to about 20 meters. Picocells can be provided to provide a number of different services (e.g., WLAN, voice, radio frequency identification (RFID) tracking, temperature and/or light control, etc.). Because a picocell covers a small area, there are typically only a few users (clients) per picocell. Picocells also allow for selective wireless coverage in small regions that otherwise would have poor signal strength when covered by larger cells created by conventional base stations.
In conventional wireless systems, picocells are created by and centered on a wireless access point device connected to a head-end controller or head-end unit. The wireless access point device includes digital information processing electronics, an RF transmitter/receiver, and an antenna operably connected to the RF transmitter/receiver. The size of a given picocell is determined by the amount of RF power transmitted by the access point device, the receiver sensitivity, antenna gain and the RF environment, as well as by the RF transmitter/receiver sensitivity of the wireless client device. Client devices usually have a fixed RF receiver sensitivity, so that the above-mentioned properties of the access point device mainly determine the picocell size.
One problem that can exist with wireless communication systems is the multi-path (fading) nature of signal propagation. This simply means that local maxima and minima of desired signals can exist over a picocell coverage area. A receiver antenna located at a maximum location will have better performance or signal-to-noise ratio (SNR) than a receiver antenna located in a minimum position. In this regard, signal processing techniques can be employed to improve the SNR of wireless data transmission in such wireless communication systems. For example, special diversity can be utilized in instances involving many access points. Other signal processing techniques include Multiple Input/Multiple Output (MIMO) techniques for increasing bit rates or beam forming for SNR, or wireless distance improvement. These techniques involve multiple antennas separated by a distance such that individual RF channels are formed between the transmitter and receiver. This distance can be less than one (1) foot in some instances.
In addition to the factors affecting SNR, variation in bandwidth response distribution among optical fiber links can also impede wireless data transmission. For example, multi-mode optical fibers (MMF) used in providing communications links can have varying distributions of bandwidth responses thus causing varying loss responses. For example, FIGS. 1A-1C illustrate exemplary MMF bandwidth response distributions to highlight the degree to which similar MMFs having similar defined characteristics can vary in loss. FIG. 1A provides a graph 2A illustrating an exemplary bandwidth response of thirteen (13) MMFs having a 62.5 micrometer (μm) core measured in a Radio-over-Fiber (RoF) link with an eight hundred fifty (850) nanometer (nm) vertical-cavity surface-emitting laser (VCSEL) measured over a range of input frequencies extending from zero (0) to six (6) GigaHertz (GHz). An exemplary distribution of the bandwidth response 3A of the thirteen (13) MMFs in the graph 2A at five (5) GHz is also illustrated in FIG. 1A to the right of graph 2A. As illustrated in this example, the loss for all measured MMFs is approximately negative eight (−8) decibels (dB) with a relatively large standard deviation between the MMFs having similar defined characteristics. Thus, if the thirteen (13) MMFs illustrated in FIG. 1A were used in a wireless communication system, the picocells formed by each of the MMFs would have a varying loss, even in the case of equal-length MMFs. This variability results in the unpredictable behavior and operation of such wireless systems.
For comparison purposes, FIG. 1B provides a graph 2B illustrating an exemplary bandwidth response of eight (8) MMFs having a fifty (50) μm core measured in an RoF link with an eight hundred fifty (850) nm VCSEL measured over a range of input frequencies extending from zero (0) to six (6) GHz. An exemplary distribution of the bandwidth response 3B for the eight (8) MMFs at five (5) GHz is also illustrated FIG. 1B to the right of graph 2B. In this example, the bandwidth loss for all measured MMFs is approximately −2.4 dB, with a smaller standard deviation of loss when compared to the standard deviation of loss for the 62.5 μm core MMFs illustrated in FIG. 1A. However, the fifty (50) μm core MMFs provided in the example of FIG. 1B may be more expensive than the 62.5 μm core MMFs provided in the example of FIG. 1A.
Comparing the loss in the 62.5 μm core MMFs in FIG. 1A to the fifty (50) μm core MMFs in FIG. 1B, the loss variation is less pronounced for fifty (50) μm core MMFs than for 62.5 μm core MMFs. Therefore, depending on the MMF, the link loss among MMFs will have a distribution similar to that illustrated in FIG. 1C.
It would be advantageous to counteract the variations in loss caused by variations in bandwidth distribution of optical fibers used as communication links in wireless communication systems. MMFs having larger variations in bandwidth distribution may be less expensive to employ in wireless communication systems, but may result in unpredictable behavior having a deleterious effect on the operation of optical fiber enabled wireless communication systems. Therefore, it would be advantageous to counteract the variations in loss of MMFs having larger variations in bandwidth distribution among optical fibers having similar defined characteristics.